Investigation of the Effects of Apple Trees Infection by Erwinia amylovora on the Expression of Pathogenesis-Related Proteins Homologous to Allergens

Pathogenesis-related (PR) proteins are induced in response to biotic and abiotic stresses. Some plant proteins, including Mal d 1, Mal d 2, and Mal d 3 in apple, are allergens. In this study, the effects of Erwinia amylovora infection of two apple cultivars, Red and Golden Delicious, on the expression of PR proteins homologous to Mal d 1, 2, and 3 were investigated.

In natural conditions trees with or without disease symptoms were sampled. In addition, seeds of the cultivars were grown in a greenhouse and seedlings were examined in three groups: 1) those inoculated by E. amylovora, 2) those inoculated by sterilized distilled water, and 3) uninoculated. Real-time PCR was used to determine expression of the Mal d 1, 2, and 3 genes (Mal d 1, 2, and 3) in infected and uninfected samples. Statistical analyses were performed using SPSS and graphs were produced by Excel. P values < 0.05 were considered significant.

 The analysis of variance showed that in natural conditions the effect of infection on the mean relative expression of Mal d 2 and 3 was significant, and more so in Red than in Golden Delicious. The analysis of variance of the greenhouse samples showed that the effect of infection on the mean relative expression of Mal d 1, 2, and 3 in both cultivars was significant.

Our results suggest that Mal d 2 is more related to plant defense than Mal d 1 or Mal d 3, and is more highly expressed in E. amylovora-resistant than in E. amylovora-sensitive cultivars.